1. Technical Field
This invention relates generally to a motor vehicle air-conditioning apparatus having an externally variable capacity type refrigerant compressor driven by the vehicle engine, and particularly to an air-conditioning apparatus which controls the idling speed of the engine based on (1) compressor torque calculated from a high-side pressure of an apparatus refrigerating circuit and (2) the value of a control current of a compressor electromagnetic capacity control valve.
2. Discussion
In Japanese Unexamined Patent Publication No. H.1-271645, a refrigerating circuit has an internally variable capacity type refrigerant compressor in which the torque needed to drive the compressor during idling is calculated on the basis of the high-side pressure of the refrigerating circuit. Engine control is carried out to stabilize the idling speed of the engine on the basis of this compressor torque. In Japanese Unexamined Patent Publication No. H.1-175517 a refrigerating circuit has an externally variable capacity type refrigerant compressor, and the torque needed to drive the compressor during idling is calculated on the basis of the cooling heat load and the intake pressure of the refrigerant compressor. Engine control is carried out to stabilize the idling speed of the engine on the basis of this compressor torque.
However, when the first related art mentioned above is applied to a refrigerating circuit having an externally variable capacity type refrigerant compressor, at times such as in spring and autumn when the cooling heat load is an intermediate heat load, the variation between the estimated compressor torque and the actual compressor torque is large. Consequently, the idling speed of the engine is not stable, and engine stalling may occur.
In the second related art mentioned above, the compressor torque is estimated on the basis of the cooling heat load and the intake pressure of the refrigerant compressor. However, this kind of calculating method is too indirect with respect to the actual compressor torque and has poor accuracy. Therefore, the idling speed of the engine is not stable, and engine stalling may occur.